Many different types of delivery systems for delivering beneficial agents such as pharmaceuticals for the prevention, treatment, and diagnosis of disease are known in the art. One type of delivery system is the subcutaneous implant which contains a supply of a beneficial agent and is implanted beneath the skin of an animal to deliver the beneficial agent over time. Some of the different types of subcutaneous implants include osmotic drug delivery implants, dissolvable or erodable pellet type implants, and diffusional implants. Some examples of osmotic delivery implant systems are described in U.S. Pat. Nos. 4,111,202; 4,111,203; and 4,203,439.
The process of placing subcutaneous osmotic implants and other types of implants under the skin is often performed by use of a trocar system which is a two-piece system, including a cannula and an obturator. With this system, an incision is first made through the skin of the patient and the cannula and obturator are inserted together through the skin. The obturator is then withdrawn leaving the cannula in place as a guide for inserting the implant. The implant is inserted through the bore of the cannula while the obturator is used to push the implant to the end of the cannula. The obturator is then used to hold the implant in a stable axial position while the cannula is being withdrawn from the patient to deposit the implant in a known position in the channel previously occupied by the cannula. The cannula and obturator are then withdrawn completely leaving the implant in place beneath the skin.
This method of insertion of an implant, including the step of removal of the obturator for insertion of the implant through the cannula followed by reinsertion of the obturator increases the possibility that sterility of the implant site will be compromised during these steps. However, it is difficult to insert the implant into the cannula prior to insertion of the cannula into the patient because the implant will tend to fail out of the cannula during the insertion process.
Known trocars can also be used with the implant in the trocar during insertion, however this method relies upon the skilled and careful use by the health care practitioner to orient the trocar so as to employ gravity to retain the implant in the cannula. Alternatively, implants capable of distortion may be held in a cannula by interference with a wall of the cannula to keep the implant in place against the force of gravity.
Known balling guns have been used in veterinary implantation procedures which retain the implant or bolus tablet in a cannula by either an interference fit or a distortion of the cannula. However, the cannulas are generally complex and expensive to manufacture.
Accordingly, it would be desirable to provide a trocar system in which an implant may be retained within the cannula in a simple and economical manner during insertion of the cannula into a patient and the implant is easily pushed out of the cannula and into the patient.